The aim of these studies is a better understanding of the cardiovascular and ventilatory responses to stimulation of chemoreceptors and a better understanding of cardiovascular effects of hypoxemia. Several studies have been done in the O2 year of this grant: 1) Effects of chemoreceptor stimulation on cutaneous and muscular vessels. 2) Effects of vagal afferent activity from cardiopulmonary receptors on the chemoreceptor reflex. 3) Mechanisms of inhibition by hypoxemia of coronary vasoconstrictor responses. 4) Effects of hypoxemia on responsiveness of the sinus node. 5) Effects of chemoreceptor stimulation on cerebral blood flow. During the next year we will attempt to answer the following questions: 1) Does hypotension potentiate cardiovascular responses to chemoreceptor stimulation in spontaneously breathing, as well as paralyzed and ventilated dogs? 2) Baroreceptor activity modulates vasoconstrictor responses in muscle to chemoreceptor stimulation. Does baroreceptor activity modulate effects of chemoreceptor stimulation on distribution of systemic blood flow (measured with microspheres)? BIBLIOGRAPHIC REFERENCES: Heistad DD, Abboud FM, Mark AL and Schmid PG: Response of Muscular and Cutaneous Vessels to Physiologic Stimulation of Chemoreceptors. Proc. Soc. Exp. Biol. Med. 148:198-202, 1975; Heistad DD, Abboud FM, Schmid PG, Mark AL and Wilson WR: Regulation of Blood Flow in Paget's Disease of Bone. J. Clin. Invest. 55:69-74, 1975.